System and Method for an Optical MEMS Transducer

ABSTRACT

According to an embodiment, an optical MEMS transducer includes a diffraction structure including alternating first reflective elements and openings arranged in a first plane, a reflection structure including second reflective elements and configured to deflect with respect to the diffraction structure, and an optical element configured to direct a first optical signal at the diffraction structure and the reflection structure and to receive a second optical signal from the diffraction structure and the reflection structure. The second reflective elements are arranged in the first plane when the reflection structure is at rest. Other embodiments include corresponding systems and apparatus, each configured to perform various embodiment methods.

This application is a continuation of U.S. patent application Ser. No.15/090,947, filed Apr. 5, 2016, which application is hereby incorporatedherein by reference in its entirety.

TECHNICAL FIELD

The present invention relates generally to microfabricated devices, and,in particular embodiments, to a system and method for an opticalmicroelectromechanical systems (MEMS) transducer.

BACKGROUND

Transducers convert signals from one domain to another and are oftenused in sensors. One common transducer operating as a sensor that isseen in everyday life is a microphone, which converts, i.e., transduces,sound waves into electrical signals. Another example of a common sensoris a thermometer. Various transducers exist that serve as thermometersby transducing temperature signals into electrical signals.

Microelectromechanical system (MEMS) based transducers include a familyof sensors and actuators produced using micromachining techniques. MEMSsensors, such as a MEMS microphone, gather information from theenvironment by measuring the change of physical state in the transducerand transferring a transduced signal to processing electronics that areconnected to the MEMS sensor. MEMS devices may be manufactured usingmicromachining fabrication techniques similar to those used forintegrated circuits.

MEMS devices may be designed to function as, for example, oscillators,resonators, accelerometers, gyroscopes, pressure sensors, microphones,and micro-mirrors. Many MEMS devices use capacitive sensing techniquesfor transducing the physical phenomenon into electrical signals. In suchapplications, the capacitance change in the sensor is converted to avoltage signal using interface circuits. Other MEMS devices use opticalsensing techniques for transducing the physical phenomenon intoelectrical signals. In such applications, an optical signal varies basedon the physical phenomenon, and the optical signal is converted into avoltage signal using a photodiode and interface circuits, for example.One such optical sensing device is an optical MEMS microphone.

SUMMARY

According to an embodiment, an optical MEMS transducer includes adiffraction structure including alternating first reflective elementsand openings arranged in a first plane, a reflection structure includingsecond reflective elements and configured to deflect with respect to thediffraction structure, and an optical element configured to direct afirst optical signal at the diffraction structure and the reflectionstructure and to receive a second optical signal from the diffractionstructure and the reflection structure. The second reflective elementsare arranged in the first plane when the reflection structure is atrest. Other embodiments include corresponding systems and apparatus,each configured to perform various embodiment methods.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a system block diagram of an embodiment MEMStransducer system;

FIGS. 2A and 2B illustrate cross-sectional side views of an embodimentoptical MEMS microphone;

FIGS. 3A and 3B illustrate cross-sectional side views of furtherembodiment elements for an embodiment optical MEMS microphone;

FIG. 4 illustrates a flowchart diagram of an embodiment method offabrication for an embodiment optical MEMS microphone;

FIGS. 5A, 5B, 5C, and 5D illustrate cross-sectional perspective views ofsteps in an embodiment method of fabrication; and

FIGS. 6A and 6B illustrate schematic top views of embodiment MEMSstructures.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of various embodiments are discussed in detailbelow. It should be appreciated, however, that the various embodimentsdescribed herein are applicable in a wide variety of specific contexts.The specific embodiments discussed are merely illustrative of specificways to make and use various embodiments, and should not be construed ina limited scope.

Description is made with respect to various embodiments in a specificcontext, namely microphone transducers, and more particularly, MEMSmicrophones. Some of the various embodiments described herein includeMEMS transducer systems, MEMS microphone systems, optical MEMSmicrophone systems, and fabrication methods of optical MEMS microphones.In other embodiments, aspects may also be applied to other applicationsinvolving any type of sensor or transducer according to any fashion asknown in the art.

In various embodiments, an optical MEMS microphone includes a laserdirected at a diffraction grating and membrane. The laser is reflectedfrom the diffraction grating and the membrane as a reflected opticalsignal that is measured by a photodetector. As the membrane deflects dueto pressure signals, such as, e.g., sound waves, the distance betweenthe diffraction grating and the membrane varies, which in turn causesthe reflected optical signal to vary. When the reflective surface of themembrane and the diffraction grating are in different planes, it may bepossible for multiple reflections to occur between the membrane and thebackplate. Such multiple reflections may affect the resulting measuredoptical signal in a way that is not consistent with the deflection ofthe membrane. Thus, according to various embodiments described herein,an optical MEMS microphone includes a membrane with a reflective surfaceor surfaces and a diffraction grating, where the reflective surface orsurfaces are formed in the same plane as the diffraction grating. Forexample, the diffraction grating may include multiple grating elementsseparated by slots to form the diffraction grating, and the membrane mayinclude reflective elements arranged in the slots between gratingelements of the diffraction grating such that the diffraction gratingand the reflective elements of the membrane are arranged in the sameplane when the membrane is un-deflected.

FIG. 1 illustrates a system block diagram of an embodiment MEMStransducer system 100 including MEMS transducer 102, applicationspecific integrated circuit (ASIC) 104, and processor 106. According tovarious embodiments, MEMS transducer 102 receives physical signal 108,generates a transduced signal, and provides the transduced signal toASIC 104. In specific embodiments, physical signal 108 is a pressuresignal, such as an acoustic pressure wave, and MEMS transducer 102 is aMEMS microphone, such as an optical MEMS microphone. In suchembodiments, MEMS transducer 102, as an optical MEMS microphone,converts physical signal 108, e.g., a pressure signal, into an analogelectrical signal that is supplied to ASIC 104. Embodiment MEMStransducers and MEMS fabrication sequences are described hereinafter.

In various embodiments, based on the analog electrical signal from MEMStransducer 102, ASIC 104 generates an output signal and provides it toprocessor 106. ASIC 104 may perform various functions. In someembodiments, ASIC 104 provides a drive signal to MEMS transducer 102 inorder to generate an optical signal and also receives an opticalmeasurement signal. In further embodiments, ASIC 104 may include abuffer circuit or an amplifier circuit. In some embodiments, ASIC 104may include additional elements such as an analog-to-digital converter(ADC). In such embodiments, ASIC 104 provides a digital signal thatcorresponds to physical signal 108 to processor 106. Further, ASIC 104may also include an I/O interface circuit for communicating through acommunication interface to processor 106.

According to various embodiments, transducer unit no includes ASIC 104and MEMS transducer 102. In such embodiments, transducer unit 110 may bea packaged device, such as a packaged microphone, including a packageopening, such as a sound port, for receiving physical signal 108.Transducer unit no may include a shared circuit board with separatesemiconductor dies for ASIC 104 and MEMS transducer 102 attached to theshared circuit board. In other embodiments, ASIC 104 and MEMS transducer102 are assembled in a chip stack as a system-on-chip (SoC), such asthrough flip-chip bonding. In still other embodiments, ASIC 104 and MEMStransducer 102 are integrated on a single semiconductor die, i.e.,monolithically integrated, as a SoC.

In various embodiments, processor 106 receives an analog or digitalelectrical signal from ASIC 104. Processor 106 may be a dedicated audioprocessor, such as an audio coder/decoder (CODEC). In other embodiments,processor 106 may be a general purpose processor. In such variousembodiments, processor 106 may be a microprocessor, a digital signalprocessor (DSP), or a field programmable gate array (FPGA). Inalternative embodiments, processor 106 is formed of discrete logiccomponents.

According to various embodiments, ASIC 104 may provide a single signal,such as a single-ended signal, or a differential single to processor 106that is representative of physical signal 108. In other embodiments,ASIC 104 may provide signals to processor 106 using variouscommunication protocols including data or clock lines. Further, invarious embodiments, MEMS transducer 102 may provide a single signal,such as a single-ended signal, or a differential signal to ASIC 104 thatis representative of physical signal 108.

FIGS. 2A and 2B illustrate cross-sectional side views of an embodimentoptical MEMS microphone 103, which is one implementation of MEMStransducer 102. Specifically, FIG. 2A illustrates an operating principleand FIG. 2B illustrates an expanded view of embodiment structures.According to various embodiments, optical MEMS microphone 103 includessubstrate 112, backplate 116, membrane 120, laser 126, and photodiode128. In various embodiments, laser 126 emits incident optical signal 130directed at diffraction grating 124 in backplate 116. Membrane 120includes reflective elements 140 formed in the same plane as diffractiongrating 124. Reflective elements 140 are omitted from FIG. 2A for easeof illustration, but are shown in expanded view 141 in FIG. 2B. Thus,incident optical signal 130 is reflected by diffraction grating 124 andreflective elements 140 of membrane 120 to form reflected optical signal132, which is received and measured by photodiode 128. In suchembodiments, pressure signals, such as sound waves as shown, causemembrane 120 to deflect, which produces a variation in reflected opticalsignal 132 that is based on the pressure signals received at membrane120. Further discussion of the reflection surface is discussedhereinafter, such as in reference to expanded view 141.

According to various embodiments, substrate 112 may be formed from awafer. Substrate 112 may be a semiconductor substrate, such as siliconfor example. In various embodiments, cavity 111 is formed withinsubstrate 112. Insulating layer 114 is formed on a top surface ofsubstrate 112 and backplate 116 is formed on a top surface of insulatinglayer 114. In such embodiments, insulating layer 114 may be anelectrically insulating material, such as silicon oxide, for example.Backplate 116 may be a rigid backplate. In various embodiments,backplate 116 includes structural support 122 and diffraction grating124. Structural support may be thick patterned beams or a thick layer ofsupporting material while diffraction grating 124 may be a smallerstructure with multiple slots or slits formed in parallel as adiffraction grating. In some embodiments, diffraction grating 124 isthinner than structural support 122. In other embodiments, diffractiongrating 124 has a same layer thickness as structural support 122. Invarious embodiments, backplate 116 may be formed of a conductive ornon-conductive material. For example, backplate 116 is formed ofpolysilicon in some embodiments.

According to various embodiments, spacing structure 118 is formed on topof backplate 116 and supports membrane 120. Spacing structure 118 may bean electrically insulating material, such as silicon oxide, for example.In some embodiments, spacing structure 118 is formed of a same materialas insulating layer 114. Membrane 120 may be formed of a conductive ornon-conductive material. For example, membrane 120 is formed ofpolysilicon in some embodiments. In some embodiments, membrane 120 isformed of a same material as backplate 116.

According to various embodiments, laser 126 is a light emitting diode(LED) laser. In further embodiments, laser 126 includes multiple LEDlasers arranged in parallel. In various embodiments, photodiode 128 mayinclude multiple photodiode structures arranged together. In alternativeembodiments laser 126 may include any type of optical signal generator,such as any source of coherent light, and photodiode 128 may include anytype of optical signal detector. In such various embodiments, laser 126may be any type of laser, or, alternatively, laser 126 may be replacedby any type of LED. Photodiode 128 may be implemented using any type ofphotodetector. In some embodiments, photodiode 128 is implemented usingone or more charged coupled devices (CCDs).

According to various embodiments, reflective elements 140 are formed inthe same plane as diffraction grating 124, as shown in expanded view 141in FIG. 2B. Expanded view 141 depicts membrane 120 and diffractiongrating 124 in detail. In various embodiments, membrane 120 includesmembrane layer 142 and reflective elements 140, which include supportlayer 144 and reflective coating 148. Diffraction grating 124, as partof backplate 116, includes grating structures 150, which includebackplate layer 146 and reflective coating 152.

According to various embodiments, membrane layer 142 extends down tosupport layer 144. In such embodiments, membrane layer 142 may be formedwith vias extending down to support layer 144 in order to connectreflective elements 140 to membrane layer 142. In other embodiments,another connection structure may be formed between support layer 144 andmembrane layer 142. In some embodiments, reflective coating 148 andreflective coating 152 are separate material coatings or material layersapplied to support layer 144 and backplate layer 146, respectively.Alternatively, reflective coating 148 and reflective coating 152 aresurfaces of support layer 144 and backplate layer 146, respectively, andare formed of a same material.

In various embodiments, reflective coating 148 and reflective coating152 are implemented using one or more metals. For example, in someembodiments, reflective coating 148 and reflective coating 152 includegold, aluminum, silver, or titanium, such as titanium nitride. Inalternative embodiments, reflective coating 148 and reflective coating152 are implemented using dielectric materials as a dielectric mirror.In such embodiments, reflective coating 148 and reflective coating 152may be implemented as a dielectric stack including alternating high andlow refractive index materials. Further, the layers selected for thedielectric stack may be selected based on the wavelength of the lightemitted from laser 126.

According to various embodiments, reflective elements 140 is connectedto membrane layer 142 in order to deflect with deflections of membrane120. As shown, reflective elements 140 are formed in the same planeextending horizontally as grating structures 150 and are arranged inthat same plane when membrane 120 is at rest. Grating structures 150 maybe long parallel beams with slots between each of the long parallelbeams in which reflective elements 140 are arranged.

According to various embodiments, as membrane 120, and correspondinglyreflective elements 140, deflects, diffraction grating 124 with gratingstructure 150 is stationary. For example, structural support 122 is arigid structure with large openings for reducing the resistance tofluidic transport and supporting diffraction grating 124. In suchembodiments, structural support 122 includes multiple thick supportbeams or a perforated rigid plate. As membrane 120 deflects, reflectivecoating 148 and reflective coating 152, which form reflective surfacesfor incident optical signal 130, are offset from each other. The offsetbetween reflective coating 148 and reflective coating 152 produces aphase shift difference in the reflected beams that results in avariation in the intensity of the combined reflected beams as reflectedoptical signal 132. In such embodiments, deflections of membrane 120,which are based on incident pressure signals, produce correspondingvariations in reflected optical signal 132 as reflective elements 140deflect with membrane 120.

In applications where a reflective surface of the membrane is not in thesame plane as the reflective surface of the backplate when the membraneis at rest, incident optical signals may be reflected and combined asdescribed hereinabove. In such applications, however, there is a higherprobability that some reflected optical signals will reflect a secondtime off the backside of the backplate. Thus, embodiments describedherein include reflective elements attached to a deflectable membrane,such as reflective elements 140 attached to membrane 120, and formed ina same plane as a reflective surface of the backplate, such asreflective coating 152 on grating structure 150. Various further detailsin relation to embodiment structures, materials, and fabrication methodsfor embodiment MEMS transducers, such as optical MEMS microphone 103,are described hereinafter in reference to the other figures.

FIG. 3A and 3B illustrate cross-sectional side views of furtherembodiment elements for an embodiment optical MEMS microphone.Specifically, FIG. 3A illustrates portion 160 a including part ofmembrane 120 and part of diffraction grating 124, and FIG. 3Billustrates portion 160 b including part of membrane 120 with addedventilation openings 164 and part of diffraction grating 124. Portion160 a and portion 160 b may be part of MEMS transducer 102 or opticalMEMS microphone 103, as described hereinabove in reference to FIGS. 1,2A, and 2B. According to various embodiments, membrane 120 includesconnecting vias 162 that connect membrane 120 to reflective elements140. For example, membrane 120 is a conductive material such aspolysilicon in some embodiments. In such embodiments, connecting vias162 are polysilicon vias extending from membrane layer 142 to reflectiveelements 140.

In various embodiments, any number of reflective elements 140 may beincluded. For example, reflective elements 140 may be included for eachslot between grating structures 150. In some embodiments, up to 100slots and 100 reflective elements 140 are included. In otherembodiments, up to 50 slots and 50 reflective elements 140 are included.In particular embodiments, up to 20 slots and 20 reflective elements 140are included. In such various embodiments, connecting vias 162 areincluded in number matching the number of reflective elements 140.

In alternative embodiments, connecting vias 162 may be replaced by otherstructures (not shown). For example, membrane layer 142 may be formed intrenches extending down to the area between grating structures 150. Inanother embodiment, a separate material from membrane layer 142 may beformed from reflective elements 140 to membrane layer 142.

According to various embodiments, membrane 120 may also includeventilation openings 164 between connecting vias 162, as shown byportion 160 b in FIG. 3B. As membrane 120 deflects, enclosed volume 166above grating structures 150, below membrane layer 142, and enclosed byconnecting vias 162 may increase or decrease. As enclosed volume 166increases or decreases, damping of the motion of membrane 120 may occur.In various embodiments, ventilation openings 164 in membrane 120 providefluidic transport into and out of enclosed volume 166, as shown byportion 160 b in FIG. 3B. In such embodiments, damping of the motion ofmembrane 120 may be reduced by ventilation openings 164.

FIG. 4 illustrates a flowchart diagram of an embodiment method offabrication 200 for an embodiment optical MEMS microphone, such asdescribed hereinabove in reference to MEMS transducer 102 or opticalMEMS microphone 103 in FIGS. 1, 2A, and 2B. FIGS. 5A, 5B, 5C, and 5Dillustrate cross-sectional perspective views of steps in method offabrication 200. According to various embodiments, method of fabrication200 includes steps 202-220. In such various embodiments, step 202includes providing substrate 302, as illustrated by intermediatestructure 300 a in FIG. 5A, which illustrates the intermediate structureafter completing step 208.

In various embodiments, substrate 302 is a semiconductor substrate.Substrate 302 may be doped for improved conductivity in someembodiments. In particular embodiments, substrate 302 is silicon.Particularly, substrate 302 may be monocrystalline silicon. Inalternative an embodiment, substrate 302 is germanium. In still anotheralternative embodiment, substrate 302 is carbon. In further alternativeembodiments, substrate 302 is a compound semiconductor such as galliumarsenide, silicon carbide, silicon germanium, indium phosphide, orgallium nitride. In still further alternative embodiments, substrate 302may be other semiconductive or conductive substrate materials as areknown to those of skill in the art. In particular alternativeembodiments, the substrate may include organic materials such as glassor ceramic. Substrate 302 may be a wafer.

Following step 202, step 204 includes depositing first oxide layer 304.Intermediate structure 300 a of step 208, as illustrated in FIG. 5A,illustrates first oxide layer 304. First oxide layer 304 may include anoxide, a nitride, or an oxynitride. For example, first oxide layer 304may be a thermally grown silicon oxide, e.g., silicon dioxide, or atetraethyl orthosilicate (TEOS) oxide. Alternatively, first oxide layer304 may be silicon nitride. In various embodiments, first oxide layer304 may be deposited or grown. In some embodiments, first oxide layer304 may be deposited by applying a chemical vapor deposition (CVD)process, a physical vapor deposition (PVD) process, an atomic layerdeposition (ALD) process, or a wet or dry oxidation of the substrate. Inparticular embodiments, first oxide layer 304 is formed as a TEOS oxide.According to particular embodiments, first oxide layer 304 is formed asa material that is electrically insulating, has strong adhesionproperties with the material of substrate 302, includes low intrinsicstress, and has an available high selectivity etch process for thematerial of substrate 302 (in order to serve as an etch stop duringetching of substrate 302).

According to various embodiments, following step 204 and before step206, a reflective coating or layer may be deposited and patterned. Forexample, reflective coating 148 and reflective coating 152 as describedhereinabove in reference to FIGS. 2A and 2B may be deposited andpatterned after step 204. In such embodiments, any of the methodsdescribed in reference to step 204 may be used to deposit the reflectivecoating or layer. Further, the reflective coating or layer may bepatterned using photolithographic processes or by using selectivedeposition techniques, such as described hereinafter in reference tostep 208.

In various embodiments, step 206 includes depositing backplate layer306. Intermediate structure 300 a of step 208, as illustrated in FIG.5A, illustrates backplate layer 306. Backplate layer 306 may includeconductive or nonconductive material. In embodiments where backplatelayer 306 is a conductive material, backplate layer 306 may be a dopedor undoped semiconductor material. In particular embodiments, backplatelayer 306 is polysilicon or monocrystalline silicon. Backplate layer 306may be in situ doped or may undergo a dopant implantation process.

In further embodiments where backplate layer 306 is a conductivematerial, the conductive material may be a metallic material. Backplatelayer 306 may include a pure metal, an alloy, or a compound. In someembodiments, backplate layer 306 includes one or more of the elementschosen from the group consisting of aluminum, copper, and nickel. Inspecific embodiments, backplate layer 306 includes pure aluminum,aluminum alloy, aluminum compound, pure copper, copper alloy, coppercompound, pure nickel, nickel alloy and nickel compound. In one specificembodiment, backplate layer 306 is an aluminum alloy with silicon andcopper. In other embodiments, the conductive material may include aconductive polymer.

In further embodiments, backplate layer 306 is a non-conductive materialsuch as an oxide, nitride, or oxynitride. In still further embodiments,backplate layer 306 is a non-conductive polymer. Backplate layer 306 maybe a layer stack including conductive and non-conductive materials. Inone such embodiment, backplate layer 306 includes a stack of siliconnitride, polysilicon, and silicon nitride.

In various embodiments, backplate layer 306 may be deposited indifferent ways such as sputtering, PVD, CVD, or ALD. Backplate layer 306may be deposited as a single step. When backplate layer 306 is ametallic material, it is possible that backplate layer 306 is depositedby a galvanic deposition. In various embodiments, backplate layer 306may be deposited or grown using any of the techniques describedhereinabove in reference to first oxide layer 304 in step 204. Inparticular embodiments, backplate layer 306 is deposited using CVD.

According to various embodiments, step 208 includes patterning backplatelayer 306. Intermediate structure 300 a of step 208, as illustrated inFIG. 5A, illustrates backplate layer 306 after patterning in step 208.In various embodiments, step 208 may include various patterningtechniques such as photolithographic techniques or selective deposition.In some embodiments, step 208 includes depositing a photoresist,exposing the photoresist to a mask pattern, and developing thephotoresist. Once the photoresist has been developed, step 208 includesetching backplate layer 306 based on the patterned photoresist.

Etching backplate layer 306 may include a wet chemistry etch or a drychemistry etch. For example, when backplate layer 306 includes asemiconductor, e.g., polysilicon or a doped semiconductor such as dopedpolysilicon, backplate layer 306 may be etched with KOH or acidsolutions of HNO₃ and HF. In another embodiment, a plasma process withchlorine or fluorine delivered by SF₆ or Cl₂ may be used to etchbackplate layer 306. In alternative embodiments, etching backplate layer306 may include a reactive ion etch (RIE) process. For an RIE process,an etch mask may be formed on the top surface of backplate layer 306with the desired pattern. For example, the etch mask may be aphotoresist material, an oxide layer, e.g., silicon dioxide, or anitride layer patterned as the etch mask. Although backplate layer 306is referred to as the backplate layer, backplate layer 306 may includeportions that are disconnected from the backplate and will be connectedto the membrane (from membrane layer 310), as will be described furtherhereinafter in reference to FIGS. 4, 5B, 5C, and 5D.

Following step 208, step 210 includes depositing second oxide layer 308.In various embodiments, step 210 may include any of the depositiontechniques and materials described hereinabove in reference todepositing first oxide layer 304 in step 204. Intermediate structure 300b of step 216, as illustrated in FIG. 5B, illustrates second oxide layer308. In particular embodiments, second oxide layer 308 is a TEOS oxide.

In various embodiments, step 212 includes patterning second oxide layer308. In such embodiments, patterning second oxide layer 308 includesforming vias 312 in second oxide layer 308 over portions of backplatelayer 306. Intermediate structure 300 b of step 216, as illustrated inFIG. 5B, illustrates vias 312 formed in second oxide layer 308. Invarious embodiments, step 212 may include any of the etching andpatterning techniques described hereinabove in reference to patterningbackplate layer 306 in step 208.

According to various embodiments, step 214 includes depositing membranelayer 310. Intermediate structure 300 b of step 216, as illustrated inFIG. 5B, illustrates membrane layer 310 deposited on second oxide layer308. In various embodiments, step 214 may include any of the depositiontechniques and materials described hereinabove in reference todepositing backplate layer 306 in step 206. In particular embodiments,membrane layer 310 is polysilicon. In alternative embodiments, step 214may include depositing a first material, such as for filling vias 312,and a second different material as membrane layer 310.

In various embodiments, step 214 includes depositing a conformal layeron second oxide layer 308 and in vias 312. In particular embodiments,step 214 includes using CVD to deposit a conformal polysilicon layer. Inalternative embodiments, step 214 includes depositing a non-conformallayer on second oxide layer 308 that fills vias 312.

According to various embodiments, step 216 includes patterning membranelayer 310. Intermediate structure 300 b of step 216, as illustrated inFIG. 5B, illustrates membrane layer 310 after patterning in step 216. Invarious embodiments, membrane layer 310 is etched in order to be formedover backplate layer 306. Step 216 may also include forming openings inmembrane layer 310 between vias 312 in order to form ventilationopenings, such as ventilation openings 164 as described hereinabove inreference to FIG. 3B. In various embodiments, step 216 may include anyetching and patterning techniques described hereinabove in reference topatterning backplate layer 306 in step 208.

Following step 216, additional steps (not shown) may be included fordepositing and patterning a contact layer or contact layers. The contactlayer is a conductive layer for forming contact lines and contact pads.In such embodiments, forming the contact layer may include depositingthe contact layer by sputtering, PVD, CVD, ALD, or galvanic deposition.In various embodiments, the contact layer may include one or more of theelements from the group consisting of aluminum, nickel, copper, gold,platinum, and titanium. Further, the contact layer or layers may bepatterned to form contact pads and contact lines. In other embodiments,contact pads may be formed using a silicide.

According to various embodiments, step 218 includes performing abackside etch of substrate 302 by etching from the back surface orbackside of substrate 302. Intermediate structure 300 c of step 218, asillustrated in FIG. 5C, illustrates cavity 314 in substrate 302 afteretching in step 218. In such embodiments, substrate 302 is etched instep 218 with a directional etch. For example, substrate 302 is etchedwith a Bosch process etch. This backside etch is applied such thatsubstrate 302 is removed under backplate layer 306 and membrane layer310. In specific embodiments, the backside etch is stopped by firstoxide layer 304.

In alternative embodiments, the backside of substrate 302 is etched witha wet etch using, for example, KOH. In another embodiment the backsideof substrate 302 is etched with a combination of dry etch and subsequentwet etching with a higher selectivity of substrate 302, such as a highersilicon selectivity, for example, versus the etch rate of first oxidelayer 304, for example.

Following step 218, step 220 includes performing a release etch byremoving first oxide layer 304 beneath backplate layer 306 and secondoxide layer 308 between backplate layer 306 and membrane layer 310.Intermediate structure 300 d of step 220, as illustrated in FIG. 5D,illustrates membrane layer 310 and backplate layer 306 after etching instep 220. In such embodiments, first oxide layer 304 beneath backplatelayer 306 and second oxide layer 308 between backplate layer 306 andmembrane layer 310 are removed with a wet etch or a dry etch. Forexample, first oxide layer 304 and second oxide layer 308 are etched byapplying an HF based solution or vapor. First oxide layer 304 and secondoxide layer 308 may be removed using any of the etching techniquesdescribed hereinabove in reference to patterning backplate layer 306 instep 208.

In various embodiments, after completing step 220, membrane layer 310 isreleased and free to move. Further, reflective elements 316, which areportions of backplate layer 306, are attached to membrane layer 310 andmove with membrane layer 310. In such embodiments, following the releaseetch of step 220, reflective elements 316 are arranged in the same planeas backplate layer 306 when membrane layer 310 is in the at restposition (un-deflected). In various embodiments, a reflective layer orcoating may be applied to the bottom surface of backplate layer 306 andreflective elements 316. The reflective layer may include any of thematerials described hereinabove in reference to reflective coating 148and reflective coating 152 in FIGS. 2A and 2B. In different embodiments,the reflective layer may be formed between step 204 and step 206 (asdescribed hereinabove) or after step 220.

Various additional steps or modifications may be included in method offabrication 200, as will be readily appreciated by those of skill in theart. In different embodiments, depending on applications, variousadditional materials and fabrication techniques known to those of skillin the art may be applied to the various steps of method of fabrication200. Such modifications are envisioned for various embodiments.

FIGS. 6A and 6B illustrate schematic top views of embodiment MEMSstructures. Specifically, MEMS structure 320 a illustrates backplatelayer 306 after patterning in step 208 and MEMS structure 320 billustrates membrane layer 310 after patterning in step 216, asdescribed hereinabove in reference to FIGS. 4, 5A, 5B, 5C, and 5D. Invarious embodiments, backplate layer 306 is patterned to includediffraction grating 322 supported by support beams 324, as similarlydescribed hereinabove in reference to diffraction grating 124 andstructural support 122 in FIGS. 2A and 2B. In other embodiments,backplate layer 306 may include diffraction grating 322 supported by aperforated support plate (not shown).

According to various embodiments, membrane layer 310 is formed overbackplate layer 306 as described hereinabove in reference to FIGS. 4,5A, 5B, 5C, and 5D. Further, membrane layer 310 may include extensionregion 326, which includes vias extending to slots in diffractiongrating 322, as described hereinabove in reference to vias 312 andreflective elements 316 in FIGS. 4, 5A, 5B, 5C, and 5D, for example. Asshown, extension region 326 is formed over diffraction grating 322.

According to an embodiment, an optical MEMS transducer includes adiffraction structure including alternating first reflective elementsand openings arranged in a first plane, a reflection structure includingsecond reflective elements and configured to deflect with respect to thediffraction structure, and an optical element configured to direct afirst optical signal at the diffraction structure and the reflectionstructure and to receive a second optical signal from the diffractionstructure and the reflection structure. The second reflective elementsare arranged in the first plane when the reflection structure is atrest. Other embodiments include corresponding systems and apparatus,each configured to perform various embodiment methods.

In various embodiments, the diffraction structure further includes aventilated support structure attached to an anchor, and a diffractiongrating supported by the ventilated support structure. In suchembodiments, the diffraction grating includes the first reflectiveelements and the openings. The reflection structure may further includea deflectable membrane layer offset from the diffraction structure, anda plurality of extension structures attached to the deflectable membranelayer, where each extension structure of the plurality of extensionstructures extends towards an opening of the diffraction structure, andeach of the second reflective elements is attached to an extensionstructure of the plurality of extension structures inside an opening ofthe diffraction structure. In some embodiments, the deflectable membranelayer and the plurality of extension structures are formed of a samefabricated layer disposed in a single fabrication step. In furtherembodiments, the deflectable membrane layer further includes a pluralityof openings, each opening of the plurality of openings arranged betweentwo extension structures of the plurality of extension structures.

In various embodiments, the optical MEMS transducer further includes alaser configured to transmit a first optical signal at the diffractionstructure, and a photodiode configured to receive a second opticalsignal from the diffraction structure and the reflection structure. Insome embodiments, the optical MEMS transducer further includes asubstrate including a cavity extending completely through the substratefrom a top surface of the substrate to a bottom surface of thesubstrate, where the diffraction structure and the reflection structureare arranged on the top surface of the substrate above the cavity.

According to an embodiment, an optical MEMS transducer includes a rigidbackplate including a diffraction grating arranged in a first plane, adeflectable membrane including a reflective surface, a light emittingelement configured to transmit a first optical signal at the diffractiongrating, and an optical detector configured to detect a second opticalsignal from the diffraction grating and the reflective surface. Thereflective surface is arranged in the first plane. Other embodimentsinclude corresponding systems and apparatus, each configured to performvarious embodiment methods.

In various embodiments, the rigid backplate further includes aventilated support structure extending from the diffraction grating toan anchor. In some embodiments, the ventilated support structureincludes a perforated plate including a plurality of perforations. Theventilated support structure may include a plurality of support beamsextending radially from the diffraction grating to the anchor in someembodiments.

In various embodiments, the deflectable membrane includes a deflectablemembrane layer offset from the rigid backplate, a plurality of extensionstructures attached to the deflectable membrane layer, and a pluralityof reflective elements together including the reflective surface. Insuch embodiments, each extension structure of the plurality of extensionstructures extends towards an opening in the diffraction grating andeach reflective element of the plurality of reflective elements isattached to an extension structure of the plurality of extensionstructures inside an opening in the diffraction grating. In someembodiments, the plurality of reflective elements includes a firstdevice layer attached to each extension structure of the plurality ofextension structures, and the first device layer includes a same layerdisposed in a same fabrication step as the rigid backplate.

According to an embodiment, an optical MEMS microphone includes abackplate and a membrane. The backplate includes a ventilated supportstructure attached to an anchor, and a diffraction grating supported bythe ventilated support structure, where the diffraction grating includesa plurality of diffraction slots. The membrane includes a deflectablemembrane layer offset from the backplate, a plurality of extensionstructures attached to the deflectable membrane layer, and a pluralityof reflective elements. In such embodiments, each extension structure ofthe plurality of extension structures extends towards a diffraction slotof the plurality of diffraction slots, and each reflective element ofthe plurality of reflective elements is attached to an extensionstructure of the plurality of extension structures inside a diffractionslot of the plurality of diffraction slots. Other embodiments includecorresponding systems and apparatus, each configured to perform variousembodiment methods.

In various embodiments, the optical MEMS microphone further includes alaser configured to transmit a first optical signal at the diffractiongrating, and a photodiode configured to receive a second optical signalfrom the diffraction grating and the reflective elements. In someembodiments, the ventilated support structure includes a plurality ofsupport beams extending radially from the diffraction grating to theanchor. The deflectable membrane layer and the plurality of extensionstructures are formed of a same fabricated layer formed in a samedeposition step in further embodiments.

In various embodiments, the plurality of reflective elements, theventilated support structure, and the diffraction grating include afirst fabricated layer formed in a same deposition step. In suchembodiments, the plurality of reflective elements and the diffractiongrating may further include a reflective coating on a bottom surface ofthe first fabricated layer.

According to an embodiment, a method of fabricating an optical MEMStransducer includes forming, on a substrate, a backplate including adiffraction grating, forming a plurality of reflective elements inopenings in the diffraction grating, forming a structural material onthe backplate, patterning the structural material to include a pluralityof vias extending to the plurality of reflective elements, forming amembrane on the structural material, removing a backside portion of thesubstrate, and removing a portion of the structural material between thebackplate and the membrane. The membrane is formed over the backplateand attached to the plurality of reflective elements, and the backsideportion extends from a bottom surface of the substrate to a top surfaceof the substrate beneath the backplate. Other embodiments includecorresponding systems and apparatus, each configured to perform variousembodiment methods.

In various embodiments, forming the backplate includes depositing abackplate layer, and patterning the backplate layer to form a ventilatedsupport structure and the diffraction grating. In some embodiments,forming the membrane includes depositing a membrane layer on thestructural material and in the plurality of vias, and patterning themembrane layer. The method may further include forming a plurality ofopenings in the membrane, where each opening of the plurality ofopenings is between vias of the plurality of vias. In furtherembodiments, removing the backside portion of the substrate includesetchings using a Bosch process. In additional embodiments, the pluralityof reflective elements and the backplate are formed of a firstfabricated layer formed in a same deposition step.

Advantages of various embodiments described herein may include opticalMEMS transducers having improved performance due to implementingstructures that reduce or eliminate multiple reflections for the opticalsignal path from optical source to optical detector. Advantageously,some embodiments include optical MEMS transducers having a reflectivesurface of a rigid structure and a reflective surface of a deflectablestructure formed in a same plane. In some embodiments, advantagesinclude reduced fabrication processing efforts due to forming reflectivesurfaces of a backplate and membrane in the same plane, which requiresonly a single reflective layer or layer stack, as opposed to formingreflective surfaces of a backplate and membrane in different planes,which requires multiple reflective layers or layer stacks.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

What is claimed is:
 1. An optical microelectromechanical systems (MEMS)transducer comprising: a diffraction structure comprising alternatingfirst reflective elements and openings arranged in a first plane; and areflection structure comprising second reflective elements andconfigured to physically deflect with respect to the diffractionstructure, wherein the second reflective elements are arranged in thefirst plane when the reflection structure is at rest.
 2. The opticalMEMS transducer of claim 1, wherein the diffraction structure furthercomprises: a ventilated support structure attached to an anchor; and adiffraction grating supported by the ventilated support structure, thediffraction grating comprising the first reflective elements and theopenings.
 3. The optical MEMS transducer of claim 1, wherein thereflection structure further comprises: a deflectable membrane layeroffset from the diffraction structure; and a plurality of extensionstructures attached to the deflectable membrane layer, wherein eachextension structure of the plurality of extension structures extendstowards an opening of the diffraction structure, and each of the secondreflective elements is attached to an extension structure of theplurality of extension structures inside an opening of the diffractionstructure.
 4. The optical MEMS transducer of claim 3, wherein thedeflectable membrane layer and the plurality of extension structures areformed of a same fabricated layer disposed in a single fabrication step.5. The optical MEMS transducer of claim 3, wherein the deflectablemembrane layer further comprises a plurality of openings, each openingof the plurality of openings arranged between two extension structuresof the plurality of extension structures.
 6. The optical MEMS transducerof claim 1, further comprising: a laser configured to transmit a firstoptical signal at the diffraction structure; and a photodiode configuredto receive a second optical signal from the diffraction structure andthe reflection structure.
 7. The optical MEMS transducer of claim 1,further comprising a substrate comprising a cavity extending completelythrough the substrate from a top surface of the substrate to a bottomsurface of the substrate, wherein the diffraction structure and thereflection structure are arranged on the top surface of the substrateabove the cavity.
 8. An optical microelectromechanical systems (MEMS)transducer comprising: a rigid backplate comprising a diffractiongrating arranged in a first plane; and a deflectable membrane comprisinga reflective surface, the reflective surface being arranged in the firstplane.
 9. The optical MEMS transducer of claim 8, wherein the rigidbackplate further comprises a ventilated support structure extendingfrom the diffraction grating to an anchor.
 10. The optical MEMStransducer of claim 9, wherein the ventilated support structurecomprises a perforated plate comprising a plurality of perforations. ii.The optical MEMS transducer of claim 9, wherein the ventilated supportstructure comprises a plurality of support beams extending radially fromthe diffraction grating to the anchor.
 12. The optical MEMS transducerof claim 8, wherein the deflectable membrane comprises: a deflectablemembrane layer offset from the rigid backplate; a plurality of extensionstructures attached to the deflectable membrane layer, wherein eachextension structure of the plurality of extension structures extendstowards an opening in the diffraction grating; and a plurality ofreflective elements together comprising the reflective surface, whereineach reflective element of the plurality of reflective elements isattached to an extension structure of the plurality of extensionstructures inside an opening in the diffraction grating.
 13. The opticalMEMS transducer of claim 12, wherein the plurality of reflectiveelements comprises a first device layer attached to each extensionstructure of the plurality of extension structures, and the first devicelayer comprises a same layer disposed in a same fabrication step as therigid backplate.
 14. A method of fabricating an opticalmicroelectromechanical systems (MEMS) transducer, the method comprising:forming a rigid backplate comprising a diffraction grating arranged in afirst plane; and forming a deflectable membrane comprising a reflectivesurface, the reflective surface being arranged in the first plane. 15.The method of claim 14, wherein: forming the rigid backplate comprisesforming the rigid backplate on a substrate; and forming the deflectablemembrane comprises forming a plurality of reflective elements inopenings in the diffraction grating, forming a structural material onthe rigid backplate, patterning the structural material to include aplurality of vias extending to the plurality of reflective elements,forming the deflectable membrane on the structural material, thedeflectable membrane being formed over the rigid backplate and attachedto the plurality of reflective elements, removing a backside portion ofthe substrate, the backside portion extending from a bottom surface ofthe substrate to a top surface of the substrate beneath the rigidbackplate, and removing a portion of the structural material between therigid backplate and the deflectable membrane.
 16. The method of claim15, wherein forming the rigid backplate comprises: depositing abackplate layer; and patterning the backplate layer to form a ventilatedsupport structure and the diffraction grating.
 17. The method of claim15, wherein forming the deflectable membrane comprises: depositing amembrane layer on the structural material and in the plurality of vias;and patterning the membrane layer.
 18. The method of claim 15, furthercomprising forming a plurality of openings in the deflectable membrane,each opening of the plurality of openings being between vias of theplurality of vias.
 19. The method of claim 15, wherein removing thebackside portion of the substrate comprises etchings using a Boschprocess.
 20. The method of claim 15, wherein the plurality of reflectiveelements and the rigid backplate are formed of a first fabricated layerformed in a same deposition step.